Hi,

Check out following links:

http://stackoverflow.com/questions/6284861/asp-net-prevent-double-clicking

http://www.codeproject.com/Questions/114164/Prevent-user-from-clicking-submit-multiple-times

http://stackoverflow.com/questions/926816/how-to-prevent-multiple-form-submit-from-client-side

http://forums.codeguru.com/showthread.php?t=480279

Though, the problem of duplicate entry in the database can be handled by enforcing some unique key in the table.

Thank you